1. Field of the Invention
The present invention relates to an electrophotographic photosensitive material, and particularly to an electrophotographic photosensitive material containing an azo pigment having a coupler component with a particular structure.
2. Related Art of the Invention
Hitherto, electrophotographic photosensitive materials which include selenium, cadmium sulfide or zinc oxide have been widely known as materials containing inorganic photoconductive substances.
On the other hand, known electrophotographic photosensitive materials in which organic photoconductive substances are used include materials containing low-molecular organic photoconductive substances, such as photoconductive polymers represented by poly-N-vinylcarbazole, 2,5-bis(p-diethylaminophenyl)-1,3,4-oxazole and the like, and materials comprising combinations of these organic photoconductive substances and various types of dyes and pigments.
Electrophotographic photosensitive materials in which organic photoconductive substances are used have certain advantages in that they exhibit good properties with respect to film formation and a very high degree of productivity. Further, they can be produced by employing a coating process and are capable of providing inexpensive photosensitive materials. Since such electrophotographic photosensitive materials also offer the advantage that their color sensitivity can be freely controlled by appropriately selecting sensitizers used, such as dyes and pigments, their use has been investigated in a wide range of fields. In particular, function separated photosensitive materials have been recently developed in which an organic photoconductive pigment is used in a charge generation layer and a charge transport layer comprising the above described photoconductive polymer or low-molecular organic conductive substance is laminated thereon. Thus, significant improvements have been achieved with respect to sensitivity and durability, which are properties unsatisfactory with conventional organic electrophotographic photosensitive materials.
Many types of pigments for use in this type of photosensitive material have been proposed. Azo pigments have been widely investigated because such pigments have various beneficial properties and can be easily synthesized by combining amine components and coupler components. However, azo pigments involve certain problems with respect to their sensitivity and potential stability when put to repeated use, and thus only few of such pigments have been brought into practical use.
Examples of known coupler components which are used in such azo pigments include naphthol AS couplers, as disclosed in Japanese Patent Laid-Open No. 37543/1972 and the like, benzcarbazole couplers, as disclosed in Japanese Patent Laid-Open No. 122967/1983 and the like, naphthalimide couplers, as disclosed in Japanese Patent Laid-Open No. 79632/1979, perinone couplers and others.